Re: [RESEND PATCH 0/6] rapidio: move Kconfig menu definition to subsystem

From: Alex Bounine
Date: Tue Jul 31 2018 - 14:22:02 EST



On 2018-07-31 11:59 AM, Russell King - ARM Linux wrote:
For the thread associated with this patch set, a review of a previous
patch for ARM posted last Tuesday on this subject asked a series of
questions about the PCI-nature of this. The review has not been
responded to.

We are dealing with this now. More appropriate to do it this time than before having reworked set.

If it is inappropriate to offer RapidIO for any architecture that
happens to has PCI, then it is inappropriate to offer it for any
ARM machine that happens to have PCI.

It is completely appropriate to use RapidIO on any architecture that has PCI/PCIe using existing PCIe-to-SRIO host bridges. Works well with Marvell and NVIDIA boards.

Confusion here is caused by the fact that there are ARM and non-ARM devices that offer on-chip RapidIO host controllers as well as PCIe. E.g. TI Keystone/KeystoneII, FSL 85xx/86xx, Xilinx and Altera FPGAs with ARM cores, Cavium on MIPS. In most cases external buses are configurable and we have to address possible combinations.

I already posted some explanation in response to your earlier comment.

In light of the lack of explanation on this point so far, I'm naking
the ARM part of this series for now.


Explanations posted.

I also think that the HAS_RAPIDIO thing is misleading and needs
sorting out (as I've mentioned in other emails, including the one
I refer to above) before rapidio becomes available more widely.

Highly likely it is used right now in a base station of mobile operator near you :)

On Tue, Jul 31, 2018 at 10:29:48AM -0400, Alexei Colin wrote:
Resending the patchset from prior submission:
https://lkml.org/lkml/2018/7/30/911

The only change are the Cc tags in all patches now include the mailing
lists for all affected architectures, and patch 1/6 (which adds the menu
item to RapdidIO subsystem Kconfig) is CCed to all maintainers who are
getting this cover letter. The cover letter has been updated with
explanations to points raised in the feedback.



The top-level Kconfig entry for RapidIO subsystem is currently
duplicated in several architecture-specific Kconfig files. This set of
patches does two things:

1. Move the Kconfig menu definition into the RapidIO subsystem and
remove the duplicate definitions from arch Kconfig files.

2. Enable RapidIO Kconfig menu entry for arm and arm64 architectures,
where it was not enabled before. I tested that subsystem and drivers
build successfully for both architectures, and tested that the modules
load on a custom arm64 Qemu model.

For all architectures, RapidIO menu should be offered when either:
(1) The platform has a PCI bus (which host a RapidIO module on the bus).
(2) The platform has a RapidIO IP block (connected to a system bus, e.g.
AXI on ARM). In this case, 'select HAS_RAPIDIO' should be added to the
'config ARCH_*' menu entry for the SoCs that offer the IP block.

Prior to this patchset, different architectures used different criteria:
* powerpc: (1) and (2)
* mips: (1) and (2) after recent commit into next that added (2):
https://www.linux-mips.org/archives/linux-mips/2018-07/msg00596.html
fc5d988878942e9b42a4de5204bdd452f3f1ce47
491ec1553e0075f345fbe476a93775eabcbc40b6
* x86: (1)
* arm,arm64: none (RapidIO menus never offered)

This set of architectures are the ones that implement support for
RapidIO as system bus. On some platforms RapidIO can be the only system
bus available replacing PCI/PCIe. As it is done now, RapidIO is
configured in "Bus Options" (x86/PPC) or "Bus Support" (ARMs) sub-menu
and from system configuration option it should be kept this way.
Current location of RAPIDIO configuration option is familiar to users of
PowerPC and x86 platforms, and is similarly available in some ARM
manufacturers kernel code trees. (Alex Bounine)

HAS_RAPIDIO is not enabled unconditionally, because HAS_RAPIDIO option
is intended for SOCs that have built in SRIO controllers, like TI
KeyStoneII or FPGAs. Because RapidIO subsystem core is required during
RapidIO port driver initialization, having separate option allows us to
control available build options for RapidIO core and port driver (bool
vs. tristate) and disable module option if port driver is configured as
built-in. (Alex Bounine)

Responses to feedback from prior submission (thanks for the reviews!):
http://lists.infradead.org/pipermail/linux-arm-kernel/2018-July/593347.html
http://lists.infradead.org/pipermail/linux-arm-kernel/2018-July/593349.html

Changelog:
* Moved Kconfig entry into RapidIO subsystem instead of duplicating

In the current patchset, I took the approach of adding '|| PCI' to the
depends in the subsystem. I did try the alterantive approach mentioned
in the reviews for v1 of this patch, where the subsystem Kconfig does
not add a '|| PCI' and each per-architecture Kconfig has to add a
'select HAS_RAPIDIO if PCI' and SoCs with IP blocks have to also add
'select HAS_RAPIDIO'. This works too but requires each architecture's
Kconfig to add the line for RapidIO (whereas current approach does not
require that involvement) and also may create a false impression that
the dependency on PCI is strict.

We appreciate the suggestion for also selecting the RapdiIO subsystem for
compilation with COMPILE_TEST, but hope to address it in a separate
patchset, localized to the subsystem, since it will need to change
depends on all drivers, not just on the top level, and since this
patch now spans multiple architectures.

Alexei Colin (6):
rapidio: define top Kconfig menu in driver subtree
x86: factor out RapidIO Kconfig menu
powerpc: factor out RapidIO Kconfig menu entry
mips: factor out RapidIO Kconfig entry
arm: enable RapidIO menu in Kconfig
arm64: enable RapidIO menu in Kconfig

arch/arm/Kconfig | 2 ++
arch/arm64/Kconfig | 2 ++
arch/mips/Kconfig | 11 -----------
arch/powerpc/Kconfig | 13 +------------
arch/x86/Kconfig | 8 --------
drivers/rapidio/Kconfig | 15 +++++++++++++++
6 files changed, 20 insertions(+), 31 deletions(-)

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2.18.0